Nick Ullett

Sheldon's latest scientific breakthrough makes him feel like a fraud – and threatens to haunt him forever. Meanwhile, Howard's romantic gesture to Bernadette causes Penny to step up her game with Leonard.

Tool Time continues to be a "jewel" despite the continued excess presence of the Binford name. Things rapidly turn sad when Al decides to take his mother out to dinner to tell her he's going to get married... and she has a heart attack and dies.